linux-kernel - RE: [PATCH 1/1] iommu/vt-d: Add MTL to quirk list to skip TE disabling

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Message-ID: <BN9PR11MB5276E104C72769026E1FA5C78CB0A@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Thu, 16 Nov 2023 08:09:14 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Baolu Lu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        "Will Deacon" <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        "Jason Gunthorpe" <jgg@...pe.ca>
CC:     "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Abdul Halim, Mohd Syazwan" <mohd.syazwan.abdul.halim@...el.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: RE: [PATCH 1/1] iommu/vt-d: Add MTL to quirk list to skip TE
 disabling

> From: Baolu Lu <baolu.lu@...ux.intel.com>
> Sent: Thursday, November 16, 2023 3:25 PM
> 
> On 2023/11/16 11:27, Tian, Kevin wrote:
> >> From: Lu Baolu <baolu.lu@...ux.intel.com>
> >> Sent: Thursday, November 16, 2023 10:23 AM
> >>
> >> @@ -5080,7 +5080,7 @@ static void quirk_igfx_skip_te_disable(struct
> >> pci_dev *dev)
> >>   	ver = (dev->device >> 8) & 0xff;
> >>   	if (ver != 0x45 && ver != 0x46 && ver != 0x4c &&
> >>   	    ver != 0x4e && ver != 0x8a && ver != 0x98 &&
> >> -	    ver != 0x9a && ver != 0xa7)
> >> +	    ver != 0x9a && ver != 0xa7 && ver != 0x7d)
> >>   		return;
> >>
> >
> > this fix alone is fine, but I found this quirk overall is not cleanly handled.
> >
> > Basically it sets iommu_skip_te_disable as true, leading to early return
> > in iommu_disable_translation():
> >
> > 	if (iommu_skip_te_disable && iommu->drhd->gfx_dedicated &&
> > 	   (cap_read_drain(iommu->cap) || cap_write_drain(iommu->cap)))
> > 		return;
> >
> > However the caller of iommu_disable_translation() is not aware of this
> > quirk and continues as if the iommu is disabled. IMHO this is problematic
> > w/o meeting the caller's assumption.
> >
> > e.g. kdump and suspend. We may want to abort those paths early in case
> > of such quirk...
> 
> I can see your point.
> 
> This fix is just to add a new device model to the established quirk
> list. All devices (including the new one) in this quirk list have
> undergone thorough verification. Therefor, I'd like to keep it as-is.
> 
> We can refine the quirk implementation in a separated patch series with
> sufficient consideration and verification. Does this work for you?

sure